Conidiation in A. cichorii Nattras is reversibly stimulated by near UV radiation (NUV .apprx. 313 nm) and inhibited by blue light (.apprx. 450 nm) and apparently is a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. Both the blue-absorbing component (presumably a flavo-protein) and the PNUV (NUV absorbing moiety) of the mycochrome system are membrane-bound. The transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53.degree. with the transition moment associated with NUV absorption in PNUV.